The inventive concepts described herein relate to semiconductor memory devices, and more particularly, to nonvolatile memory devices having flag cells and to user devices including the same.
Semiconductor memory device are generally classified as volatile or nonvolatile. Volatile semiconductor memory devices lose data stored upon entering a power-off state, while nonvolatile semiconductor memory devices retains data stored therein even during a power-off state. The nonvolatile semiconductor memory device is thus useful to retained store contents in applications where the interruption of supplied power is to be expected.
The flash memory, which is a popular type of nonvolatile memory found in computers, memory cards, and the like, is characterized in part by simultaneous electrical erasure of units (e.g. blocks) of memory cells prior to programming. Further, each memory cell of flash memory may be configured to store 1-bit data or multi-bit data. However, the number of programmed threshold voltage states increases dramatically as the number of bits per memory cell is increased. For example, in the event that 1-bit data is stored, the memory cell is programmed to have a threshold voltage belonging to one of two threshold voltage distributions (or, states). In the event that 2-bit data is stored, the memory cell is programmed to have a threshold voltage belonging to one of four threshold voltage distributions (or, states).